1. Field of the Invention
The present invention relates to technology for crystallizing a semiconductor film by irradiation with a laser beam. Further, the present invention relates to a method of manufacturing a semiconductor device using a crystallized semiconductor film.
2. Description of the Related Art
Extensive research has been conducted and many proposals have been made concerning technology for forming a crystalline silicon film by irradiating an amorphous silicon film with a laser beam and crystallizing the amorphous silicon film. Active matrix liquid crystal display devices in which a polycrystalline silicon film obtained by crystallizing an amorphous silicon film with an excimer laser is used have already been commercialized as high-resolution panels for portable telephones and the like.
Lasers used for laser annealing are broadly classified into two types, pulsed lasers and continuous wave lasers, depending on their method of oscillation. Excimer lasers are pulsed lasers. In recent years, it has been reported that crystalline silicon having large grain crystals can be formed more successfully when a continuous wave laser such as an Nd:YVO4 laser is used than when a pulsed laser such as an excimer laser is used. For example, in Non-Patent Document 1, it is disclosed that concerning crystalline silicon, grain boundaries are parallel to a scanning direction of a laser beam and a very large grain size of 3×20 μm is obtained; that the (100) orientation is dominant; and that a thin film transistor with a field-effect mobility of 532 cm2/Vs was manufactured (Akito Hara and five other authors, AM-LCD '01 DIGEST OF TECHNICAL PAPERS, 2001, pp. 227-230).